Bird feeders are prone to being accessed by a variety of animals other than the intended fowl. Foremost among the invaders is the squirrel. Despite many attempts to devise a bird feeder, either post-mounted or of the hanging type, that is resistant to being looted by the squirrel, no consistently-effective product exists. The past attempts have included weight-activated electric shock deterrent feeders, weight-activated barrier systems, as well as even greased-pole mounted feeders. Although they may prevent access by the squirrel to the bird feed initially, the squirrel has always been able to circumvent all barriers placed in its path, in time.
Although some of the failures are related to the mechanics of the design (e.g., electric system breakdown, corrosion of movable joints/components, etc.), other failures are due to the intelligence of the squirrel and the fact that squirrels may often "invade" the feeder in groups.